The Revised Wechsler Tests of Intelligence S

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Information Sheet 41
The Revised Wechsler Tests
of Intelligence
By Molly Tweedie, Psychologist
S
ome of the most frequently
used tests of intelligence for
children are those known as the
Wechsler Tests.
These tests were created by David
Wechsler and include the Wechsler
Adult Intelligence Scale, the Wechsler
Intelligence Scale for Children and the
Wechsler Preschool and Primary Scale
of Intelligence. The tests are known
respectively as the WAIS, the WISC and
the WPPSI (pronounced wipsy). The
original WISC was published in 1949 and
the WPPSI in 1967.
Since then, there have been three
revisions for the WISC and two for the
WPPSI. All three tests have been revised
recently, with the new WISC being
published in 2003 and the WPPSI in
2004.
What’s new and why?
The tests are revised regularly for a
number of reasons.
The first is to keep the content of the
tests in line with current theories about
what constitutes intelligence and how it
can be measured.
For example, in one of the previous
versions of a commonly used
intelligence test there was a question
about aesthetic preference. The
subject was shown pairs of pictures
and asked to state which picture was
preferred. One picture was a drawing
of an attractive young woman; the
other looked like an illustration from
an old book about the criminal classes.
Aesthetic preference, especially using
such a biased approach, is no longer
considered to be a significant measure
of intelligence.
The questions and general artwork are
also revised, eliminating ‘old fashioned’
questions and pictures.
The pictures have been modernised,
with clothing and hairstyles made to
look more contemporary and there is
now an ethnic mix among the drawings
of people, so they are no longer
obviously all Caucasians.
There is no longer the emphasis on
speed of performance, as it is recognised
that it disadvantaged many children,
for example, children who are anxious
or perfectionist. Surprisingly perhaps,
gifted children often achieved lower
scores on the Processing Speed tasks,
which in turn lowered their Full Scale
score.
In some cases, the order of presentation
of the questions has been changed. For
example, a question about why stamps
are put on letters has been moved from
number 13 to number 17, as many
younger children had trouble with this
question.
As well as making the questions and
pictures more relevant, the tests have
been ‘re-normed’.
This means that the test is trialled on
large groups of appropriately aged
people and the results then used to
form the new norms tables, against
which a child’s score is compared. The
score for a child who is being tested in
2006 is compared with children who
were tested in the years preceding 2003,
rather than with scores from individuals
who were tested in the 1970s.
The WISC–IV has also been part of a
massive project to provide Australian
standardisation.
As well as providing Australian norms,
so that Australian children are compared
with other Australian children rather
than American children, it has ensured
that questions and vocabulary are
appropriate; for example asking who
is Captain Cook rather than Benjamin
Franklin. Pictures have also been made
more culturally relevant: for example, a
rabbit or a possum are used rather than
a squirrel or a raccoon.
Another important reason why tests are
changed and updated is a phenomenon
known as the Flynn Effect (1984).
Put simply, James Flynn theorised
that over time, IQ scores increase by
approximately three points per decade.
The reasons for this are uncertain, but
it is hypothesised that improved health
and nutrition and longer time spent at
school, as well as changes in education
are all factors that contribute to this
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effect. Another factor that is thought to
contribute to the effect is that parents
now spend more time with their
children, stimulating their cognitive
development.
The revisions of the WISC and the WPPSI
have also extended the ceiling and the
basal levels of the test scores, by adding
further easy and difficult questions at
either end of the subtests.
This means that they discriminate better
among children who achieve either
very high or very low scores. Previously,
children who gained scores at the
extreme ends of the scale could not be
identified as clearly. The age range for
the WPPSI–III has also been extended
downwards from 4 years to 2.6 years,
with a shortened version for use with
children from 2.6 to 3.11 years.
A real benefit from the psychologist’s
point of view is that as well as the items
being made more attractive and the
questions more relevant, they are also
made easier to administer and the
testing time is shorter. The instructions
have been simplified; some subtests
removed and new ones created.
In the essentials, the new tests are very
similar to their predecessors.
They both measure verbal and
non-verbal skills and have subtests
to measure working memory and
processing speed. The WISC–IV uses the
four Index scales to create the Full Scale
score, whereas the WISC–III only used
the Verbal and the Performance scales
and although it was useful to administer
all the subtests to calculate the four
Index scores, it was not essential.
appropriate. For example, Picture
Completion, which does not require
any physical response, may be used
as a substitute for Block Design for a
child with a physical disability such as
Cerebral Palsy.
The structure of the test is hierarchical,
with the Full Scale score being the
sum of the four Index Scales, which are
created from the subtests.
Arriving at the scores
The subtests are scored according to
the criteria given in the test manual and
the raw scores are converted to scaled
scores, using the age appropriate tables,
so the results for a student who is 8
years and 5 months old are compared
with those of other students between
the ages of 8 years and 3 months to 8
years, 5 months and 30 days.
The scaled scores from the subtests are
summed and these are then used to
form the Index Scores and the Full
Scale score, again by looking up the
appropriate table in the manual.
The scaled scores for the subtests
range between one and 19, with scores
between seven and 13 being within the
average range. The Index Scores and
the Full Scale score have mean scores of
100 and the average range is between
90 and 109.
The Full Scale score is central to
identifying children who are either
developmentally disabled or gifted.
Wechsler Intelligence Scale
for Children – 4th Edition
As a single score, it is most relevant
and reliable when there is little
variability among the Index
scores that comprise it. If there are
discrepancies of 20 points or more
among the Index scores, the Full
Scale IQ becomes less meaningful
as a description of the child’s ability.
Similarly, if there are large differences
among the subtest scores that comprise
an Index Score, the single score is no
longer as meaningful as a description
of the child’s ability in that particular
area and the individual scores should be
considered.
The WISC–IV uses 10 core subtests to
create four Index Scores, which have
replaced the Verbal and Performance
Scales of the WISC–III. There are also
five supplemental subtests that can be
used either to expand the amount of
information about a particular area or to
replace a core subtest.
Because it is recognised that no
assessment is perfect, Intelligence
Quotients are generally reported as a
range (the Confidence Interval), rather
than as a single score. This predicts
that with either 90 or 95% certainty, a
student’s “true” score will fall within a
given range.
The tester may feel that a subtest
has been spoiled for some reason or
that a different subtest may be more
A student’s score may vary from one
occasion of assessment to another, but
it will generally remain within the range.
The WPPSI–III is also very similar to
its predecessor, but now includes a
Processing Speed scale as well as a
General Language scale. Reporting of
the scores has also been brought into
line with current practices by providing
percentiles and confidence intervals,
rather than a single score for results.
Information Sheet 41 – Learning Links – Helping Kids Learn
The scores tend to be more stable as
the child matures, as older children are
generally more cooperative and less
influenced by outside factors, whereas
the scores from younger children are
more vulnerable to change. They are
more susceptible to outside variables,
such as the personality of the tester,
motivation and the ability to sustain
attention for the duration of the testing.
Maturation and education also can
affect scores markedly, as can previous
exposure to testing. Practise effect
is a recognised phenomenon and
can improve a child’s score, so it is
recommended that there should be at
least two years between occasions of
assessment.
Verbal Comprehension Index
The Verbal Comprehension Index (VCI)
is ‘composed of subtests measuring
verbal abilities utilising reasoning,
comprehension and conceptualisation’
(Wechsler, 2003). It consists of three
core subtests and two supplemental
subtests.
The three core subtests and one of
the supplemental tests are similar
to those from the WISC–III, but a
new supplemental subtest has been
introduced. Arithmetic has been
removed from the Verbal scale and is
now a supplemental test for the Working
Memory Index.
The emphasis of this index is now on
reasoning and comprehension rather
than on crystallised knowledge.
However, reasoning with verbal
material still requires some level of
crystallised knowledge; for example,
a student cannot describe how two
concepts are alike unless they have prior
understanding of the words and can
access this information when required.
Perceptual Reasoning Index
This index was the Perceptual
Organisation Index of the WISC–III.
It is ‘composed of subtests measuring
perceptual reasoning and organisation
… the name change from POI in WISC–III
to PRI in WISC–IV reflects the increased
emphasis on fluid reasoning abilities in
this index’. (Wechsler, 2003, p 6).
There is less emphasis on speed of
responding and perceptual organisation
and more on fluid reasoning, with only
Full Scale Score
Verbal Comprehension
Perceptual Reasoning
Working Memory
Processing Speed
Similarities
Block Design
Digit Span
* Picture Concepts
* Letter-Number
Coding
Vocabulary
Symbol Search
Sequencing
Comprehension
* Matrix Reasoning
† Information
† Picture Completion
† *Cancellation
† * Word Reasoning
† Arithmetic
† Supplemental subtest
* New subtest
one subtest being timed and having
bonus points for speed of responding.
One of the original subtests has been
kept as a core subtest and two new
ones added. There is one supplemental
subtest, which is one of the original
WISC–III subtests.
Working Memory Index
This index was originally named the
Freedom from Distractibility Index,
which was misleading. The new name
of the index is now a more accurate
reflection of what the scale measures.
Working Memory is the ability to
temporarily retain information in
the memory, manipulate it and
achieve a result. It involves attention,
concentration, mental control
and reasoning and is an essential
component of other higher order
cognitive processes.
There are three subtests in this scale;
two core and one supplemental.
All three subtests measure verbal
working memory, but not spatial or
visual working memory. One of the
subtests is a task from the original test
and one is a new subtest, with one task
from the WISC–III being retained as a
supplemental subtest.
Processing Speed Index
This index provides a measure of the
student’s ability to correctly scan,
sequence or discriminate simple visual
information. It also measures short term
visual memory, attention and motor
coordination.
It is recognised that quick and efficient
processing of routine visual information
may conserve working memory
resources, so students who perform
well on this task have more capacity
for other cognitive tasks. The two core
subtests are from the WISC–III and a
new supplemental subtest has been
included.
Wechsler Preschool
and Primary Scale of
Intelligence – 3rd Edition
The WPPSI–III is similar to the WISC–IV in
the administration, the subtests and the
overall format of the test.
There are some differences between
the two tests, particularly reflecting the
differences in development between
preschool children and children
who have been at school for three or
more years.
Language development in young
children in particular can significantly
affect the scores on cognitive tests and
the WPPSI–III has reduced this emphasis,
by the inclusion of more picture items in
the Verbal subtests and less requirement
of longer verbal answers in the core
subtests. This is particularly the case for
the younger children (2.6–3.11 years)
where only one subtest requires verbal
responses.
A subtest measuring receptive
language, which is entirely non-verbal,
has been introduced as a core subtest
for these younger children and as a
supplemental test for the older ones.
1. Wechsler, D. (2003) Manual for the Wechsler Intelligence Scale for Children (ed. 4) San Antonio: The Psychological Corporation.
2. Crystallised knowledge refers to problem solving and factual learning that is dependent on formal schooling, whereas fluid intelligence or reasoning is
the ability to solve new problems where formal education is not of direct assistance.
3. Wechsler, D. (2003) Manual for the Wechsler Intelligence Scale for Children (ed. 4) San Antonio: The Psychological Corporation.
Information Sheet 41 – Learning Links – Helping Kids Learn
In the administration of all subtests, the
instructions have been simplified and
there are also more opportunities to
prompt or to question if a child’s answer
is unclear.
There is also a decreased emphasis
on time.
Preschool children generally have
had less exposure to the concept of
working quickly and completing a task
within a given time than have school
age children. Some tasks (Block Design,
Object Assembly) still have a time limit
in which an item is to be completed,
but there are no longer bonus points for
speed of performance.
These subtests are measures of visualspatial reasoning and problem solving,
rather than processing speed. A
Processing Speed scale, similar to that
in the WISC–IV has been introduced, but
only one of the subtests is included in
the calculation of the Full Scale score for
the older children (4+ years).
There have been further changes to
the test to accommodate the motor
development of younger children.
The WPPSI–R used thin, tile-shaped
blocks for Block Design, rather than the
cubes used in the other tests. Cubes
are now used, as they are easier for a
younger child to grasp and manipulate.
The Geometric Design, Mazes and
Animal Pegs have also been deleted,
as performance on these subtests was
strongly affected by neurological and
motor development. The prefrontal
cortex develops and changes
dramatically over this age range, so
poorer performance on these subtests
may be a result of development, rather
than of cognitive ability.
The Arithmetic subtest has also been
deleted, as exposure to pre-number
and early mathematical skills is strongly
biased by familiarity with these
concepts, so poor results may reflect
lack of exposure to the concepts of
number, as well as slower development
of the understanding of abstract ideas.
Why an IQ test?
There are three major reasons why a
child may be referred for a psychometric
test. There may be concerns about their
overall development, or because they
are struggling with acquiring basic
literacy skills or there is a query about
whether the child is gifted.
A young child may be referred
for a psychometric assessment to
help determine whether there is a
cognitive delay.
These children seem to be developing
skills more slowly than their peers
and the parents and/or professionals
involved with them may feel that
the difficulties are the result of a
developmental disability. The IQ test
will help to establish the level at which
the child is functioning cognitively. This
has implications for entrance into early
intervention programs and once they
start school, for eligibility for integration
funding or inclusion into a support class
or school.
The child may have a mild disability,
where the IQ score falls between 55
and 75.
These children may be eligible for
integration funding to enable them
to be educated in a mainstream class.
The amount of funding they receive is
determined not only by the IQ score,
but also by their overall social and self
care skills.
Many of these children cope well in the
integrated setting in their early years,
but as they get older, the discrepancy
between their development and that of
their peers with average ability becomes
larger and they will require more
support in the classroom, which may
include a modified program.
A child with an IQ score below 55
is described as having a moderate
disability.
These children generally have delays
in all areas of their development,
particularly in language and social skills.
Their needs are generally best met in a
support class or unit in a mainstream
school. Where there are behavioural
problems or more than one disability,
a School for Specific Purposes will
often provide the best support and
educational program.
The second reason a child may be
referred for assessment is because they
are having difficulty with acquiring basic
literacy skills. This may be because they
are of lower cognitive ability or they
have a specific learning problem.
The IQ test will identify the child of
lower ability, but a child with a specific
learning problem will often be of
average or above average intelligence.
The test has eliminated one cause for
the difficulty they are having, but may
not provide any clear evidence of the
learning problem.
The student with a learning problem is
best identified through achievement
or academic testing, as well as
psychometric testing.
This testing can identify whether they
have a difficulty with reading and will
help establish where the problem
lies. The scores from a test such as the
Wechsler Individual Achievement Test
– 2nd Edition (WIAT–II) can be compared
against the scores from the WISC–IV and
this will indicate whether the student
is performing at a level commensurate
with their cognitive ability, or whether
there is a discrepancy between the
scores.
Children may be referred for assessment
because of a query as to whether they
are gifted.
The Department of Education requires
that children turn five years of age on or
before the 31st of July of the year they
begin school. Parents of gifted children,
who want their child to begin school
earlier, have to provide proof that the
child is gifted.
The Department requires an IQ score,
which has to fall in the 95th percentile
or above 125 (Superior to Very Superior
range.) For a young child to cope
well at school, they need to have
good language skills and be socially
competent as well as being intellectually
gifted.
Although there are arguments as to the
need for IQ testing for children, up to
date and relevant testing is an important
tool for helping identify children’s
differing educational needs.
References
Flynn Effect – Wikipedia, the free encyclopedia.
www.Wikipedia.org/wiki/Flynn_effect
Kearney, K and Gilman, B.J. (2004) Assessment
and Testing: What about the SB5, WISC–IV and
Other Tests. www.neiu.edu/~ourgift/Archives/
Kearney_Gilman/Gilman_Closing_ statement.
htm
Prifitera, A,, Saklofske, D.H., and Weiss, L.G.(Eds)
(2005) WISC–IV. Clinical Use and Interpretation.
Massachusetts: Elsevier Academic Press
Sattler, J.M. (1992) Assessment of Children (3rd
Ed) San Diego: Jerome M Sattler, Publisher, Inc
Wechsler, D. (2003) Manual for the Wechsler
Intelligence Scale for Children (ed. 4) San
Antonio: The Psychological Corporation
Wechsler, D. (2002) Technical and Interpretive
Manual for the Wechsler Preschool and Primary
Scale of Intelligence (ed. 3) San Antonio: The
Psychological Corporation
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